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Monday, September 11, 2017

When exercise helps and when it doesn't

Activity in later life
improved short-term cognitive fitness

Johns Hopkins University Bloomberg School of Public Health

A study led by Johns Hopkins Bloomberg School of Public Health researchers that tracked activity levels of 646 adults over 30 years found that, contrary to previous research, exercise in mid-life was not linked to cognitive fitness in later years.The finding suggests that physical activity may not help
maintain cognitive function, or help avoid or delay the onset of the
debilitating conditions like dementia and Alzheimer's. Alzheimer's affects as
many as 30 million, mostly older people throughout the world. With no known
treatment or cure, researchers are trying to identify measures that might help
delay Alzheimer's onset or limit its reach.

The study, which appears online in the Journal of
Alzheimer's Disease, did find that activity levels among study participants
in the later years were associated with high cognitive function two years
later. This supports earlier research findings that exercise may help to
maintain cognitive fitness in the short term.

"This study reminds us that physical activity has all sorts
of benefits for people, including promoting cardiovascular health, managing
optimal weight levels and maintaining bone and muscle mass," says Alden L.
Gross, assistant professor in the Bloomberg School's Department of
Epidemiology. "Unfortunately it is too early for us to say the same about
exercise and Alzheimer's, especially as a possible long-term preventive
measure."

There is no known treatment or cure for Alzheimer's or dementia,
syndromes that involves declining memory, confusion and eventually limited
ability to perform daily tasks. To date, there are no preventive measures, such
as physical exercise, brain games or a diet regimen, that have been proven to
help delay or altogether prevent its onset. In the US, an estimated five
million adults are currently living with Alzheimer's, according to the Centers
for Disease Control and Prevention (CDC), and the CDC predicts that this number
will rise to 14 million by 2050.

The researchers undertook the study because of a growing
consensus that physical activity levels helps prevent Alzheimer's, however much
of the evidence for this thinking is based on cross-sectional studies that
compare responses from one group of participants with another at a given point
in time or within a very short duration, typically several years. Such studies
can be valuable for confirming associations, or links, but not at establishing
actual causation because of what is known as reverse causation: it is possible
that people who eventually develop dementia may reduce their physical activity
and exercise as dementia advances. That's where longitudinal studies, which
look at the same group of participants over a long time, are more helpful.

The researchers used data from the Johns Hopkins Precursors
study, which registered students studying at Johns Hopkins School of Medicine
between 1948 and 1964 and tracked them with annual questionnaires about their
overall health. The researchers note that the cohort's homogeneity -- students
at a selective medical school -- meant that any differences in physical
activity and later cognitive function could not be explained by other
differences among participants.

The median age for study participants was 46 years in 1978 and
77 years in 2008. Every several years, the questionnaire asked about exercise,
physical activity and physical limitations. The researchers used responses from
1978 through 2008 from 646 participants (598 men, 48 women) to calculate
so-called metabolic equivalents, which quantify physical activity levels.
Participants were also asked whether they regularly exercise to a sweat.

The team administered cognitive tests in 2008, and, using
participants' medical records, scored for dementia through 2011. The
researchers identified 28, or 4.5 percent of the cohort, to have Alzheimer's.

No physical activity measure in mid-life was associated with
late-life cognitive fitness or onset of dementia. The study confirmed findings
of other cross-sectional studies, that higher levels of physical activity and
exercise measured close in time to the cognitive testing were associated with
better cognitive functioning. The authors also looked at whether patterns of
change in physical activity levels over the life span were associated with
cognitive health and found no relationships.

The idea that exercise might play a role in preventing or
limiting Alzheimer's makes sense, the researchers say, because physical
activity, at least in mouse models, has shown less accumulation of B-amyloid
plaques, which are thought to play a role in dementia, including Alzheimer's. In addition, physical activity improves blood flow to the brain, which is
linked to better cognitive performance. This may explain why studies find that
exercise may contribute to cognitive fitness in the short term.

"These findings have implications for intervention work
moving forward," says Gross. "We still need to focus on causes and
mechanisms of Alzheimer's and dementia, since we don't yet know which
preventive measures may or may not work. For now, when I speak in the community
about Alzheimer's, I find that people take some relief in understanding that
there wasn't anything that anyone might have done to avoid a loved one
developing Alzheimer's. Of course, the goal for researchers is to identify
factors that may help older people maintain their cognitive function into their
later years. More long-term studies like the Precursors study are needed."